1. Field Of The Invention
The present invention relates generally to the fracturing of wells, and more particularly to a mixer system for mixing concentrated liquid gelling agent and water in an efficient manner to provide rapid and efficient hydration of the concentrated liquid gelling agent.
2. Description Of The Prior Art
It is well known in the oil industry to fracture wells using gelled fracturing fluids to carry sand and other particulate materials into the subterranean formation of the well.
Originally, such gelled fracturing fluids were mixed from dry polymer materials. More recently, it has become common to utilize a concentrated liquid gelling agent which carries the polymer phase dispersed in an oil based fluid. That concentrated liquid gelling agent is mixed with water shortly before the sand or other particulate material is added. Then the sand laden gel is pumped into the well. In order for the gelled fracturing fluid to develop its full viscosity and thus its full sand carrying capacity, it is necessary for the polymer material contained in the concentrated liquid gelling agent to be hydrated, i.e., to absorb water. In the absence of intense shear complete hydration of the gel does not occur for fifteen minutes or more after the guar based polymer is mixed with water. Therefore, continuous mixing of concentrated liquid gelling agent can require holding vessels of very large volumes so that sufficient hydration for proppant support will have occurred before the fluid enters the fracturing blender tub or sand tub.
The time required for the hydration of the gel can be reduced by subjecting the gel to high shear.
The prior art approach to increasing the rate of hydration is represented by U.S. Pat. No. 4,828,034 to Constien et al. which discloses a system utilizing a high shear pump to pump the gel through a static mixer to impart shear energy to the gel. Systems like that of the Constien et al. patent, however, as actually used in the field, still typically require a blender tub operating volume on the order of 200 barrels in order to provide sufficient residence time. A 200-barrel blender tub makes an extremely large unit which is difficult to transport to the field.
Thus, there is still a need for an efficient compact system for mixing of concentrated liquid gelling agents and water to form fracturing fluids.